It is known that a glass material that has been softened by heating can be press molded with a pressing mold to transfer the shape of the molding surface to the glass material, thereby producing an optical element such as a glass lens. The optically functional surfaces of an optical element that has been formed by press molding possess the desired optical performance without being subjected to mechanical processing such as polishing.
Patent Reference 1 discloses a method of manufacturing pressed lenses by placing a glass material (preform), the surface of which has been coated with a silicon oxide film, in a pressing mold, and press molding the glass material at a temperature at which it is in a softened state. This method is described as preventing fusion of the mold and glass during press molding, and preventing the precipitation of reduced particles due to reduction of PbO contained in the glass.
Patent Reference 2 discloses a method for molding optical glass elements by forming a thin layer comprised primarily of SiO2 in the center portion of the surface of a glass element in advance, and placing the glass material in a pressing mold and conducting press molding. This method is considered to yield an optical element having an optically functional surface such that the occurrence of surface cracks is avoided and no clouding is generated in the center portion.
Patent Reference 3 discloses an optical element having a glass core that has been premolded, on the surface of which double surface layers are formed. The first surface layer is formed as a film on the surface of the glass core at a temperature greater than or equal to the glass transition point while the glass core material is in a state of reduced pressure, and the second surface layer is formed as a film on the first outer layer by sputtering a vapor deposition-use glass material. Patent Reference 3 also discloses a method for manufacturing an optical element. A glass material comprising 70 to 90 mass % of SiO2 is employed as the vapor deposition-use glass material to form the second outer layer. According to the invention, even when a glass containing strongly reactive glass or highly volatile glass components is employed as the glass material, an optical component can be obtained that is free of surface cracks, fusion, and clouding.